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Commitce6a71f

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Use vectored I/O to fill new WAL segments.
Instead of making many block-sized write() calls to fill a new WAL filewith zeroes, make a smaller number of pwritev() calls (or variousemulations). The actual number depends on the OS's IOV_MAX, whichPG_IOV_MAX currently caps at 32. That means we'll write 256kB per callon typical systems. We may want to tune the number later with moreexperience.Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>Reviewed-by: Andres Freund <andres@anarazel.de>Discussion:https://postgr.es/m/CA%2BhUKGJA%2Bu-220VONeoREBXJ9P3S94Y7J%2BkqCnTYmahvZJwM%3Dg%40mail.gmail.com
1 parent13a021f commitce6a71f

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  • src/backend/access/transam

1 file changed

+22
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‎src/backend/access/transam/xlog.c

Lines changed: 22 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -48,6 +48,7 @@
4848
#include"pg_trace.h"
4949
#include"pgstat.h"
5050
#include"port/atomics.h"
51+
#include"port/pg_iovec.h"
5152
#include"postmaster/bgwriter.h"
5253
#include"postmaster/startup.h"
5354
#include"postmaster/walwriter.h"
@@ -3270,7 +3271,6 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
32703271
XLogSegNoinstalled_segno;
32713272
XLogSegNomax_segno;
32723273
intfd;
3273-
intnbytes;
32743274
intsave_errno;
32753275

32763276
XLogFilePath(path,ThisTimeLineID,logsegno,wal_segment_size);
@@ -3317,6 +3317,9 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
33173317
save_errno=0;
33183318
if (wal_init_zero)
33193319
{
3320+
structioveciov[PG_IOV_MAX];
3321+
intblocks;
3322+
33203323
/*
33213324
* Zero-fill the file. With this setting, we do this the hard way to
33223325
* ensure that all the file space has really been allocated. On
@@ -3326,15 +3329,28 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
33263329
* indirect blocks are down on disk. Therefore, fdatasync(2) or
33273330
* O_DSYNC will be sufficient to sync future writes to the log file.
33283331
*/
3329-
for (nbytes=0;nbytes<wal_segment_size;nbytes+=XLOG_BLCKSZ)
3332+
3333+
/* Prepare to write out a lot of copies of our zero buffer at once. */
3334+
for (inti=0;i<lengthof(iov);++i)
33303335
{
3331-
errno=0;
3332-
if (write(fd,zbuffer.data,XLOG_BLCKSZ)!=XLOG_BLCKSZ)
3336+
iov[i].iov_base=zbuffer.data;
3337+
iov[i].iov_len=XLOG_BLCKSZ;
3338+
}
3339+
3340+
/* Loop, writing as many blocks as we can for each system call. */
3341+
blocks=wal_segment_size /XLOG_BLCKSZ;
3342+
for (inti=0;i<blocks;)
3343+
{
3344+
intiovcnt=Min(blocks-i,lengthof(iov));
3345+
off_toffset=i*XLOG_BLCKSZ;
3346+
3347+
if (pg_pwritev_with_retry(fd,iov,iovcnt,offset)<0)
33333348
{
3334-
/* if write didn't set errno, assume no disk space */
3335-
save_errno=errno ?errno :ENOSPC;
3349+
save_errno=errno;
33363350
break;
33373351
}
3352+
3353+
i+=iovcnt;
33383354
}
33393355
}
33403356
else

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